The present invention relates, in general, to semiconductor devices and, more particularly, to a composite dielectric layer for electrically insulating two conductive terminals of a semiconductor device.
A typical bipolar semiconductor device is formed on a silicon substrate such as, for example, a lightly-doped epitaxial layer, and includes an emitter terminal and a base terminal that each contact diffusion regions in the substrate. One material typically used for forming these terminals is polysilicon, and the terminals usually have metal contacts formed on their top surface. The emitter terminal is typically formed through an opening in an insulating layer overlying the substrate and is separated from the base terminal by a thin dielectric layer.
One prior dielectric material used to electrically separate the emitter and base terminals is silicon nitride. However, the use of silicon nitride causes several adverse effects in the operation of the bipolar device. One significant adverse effect is an excessive leakage current between the emitter and base terminals. The leakage current may flow by numerous leakage paths, such as through a nitride defect, and significantly degrades device performance, quality, and reliability. Another adverse effect of a silicon nitride dielectric is the formation of stress cracks due to the high mechanical stress of the deposited silicon nitride layer.
Accordingly, it is desirable to have a dielectric layer for separating the emitter and base terminals of a bipolar device that reduces emitter-base leakage and stress cracks in the dielectric layer.